The present invention relates to gas turbine engines, and in particular, to air turbine starters on gas turbine engines. Gas turbine engines typically have at least one spool that includes a compressor and a turbine. When a gas turbine engine is burning fuel and operating, the spool rotates at a high speed without further assistance. However, when a gas turbine engine is started, the spool typically needs assistance to begin rotation. Various starters have been devised to start the spool rotating.
In some gas turbine engines, an air turbine starter is used to start rotation of the spool. The air turbine starter has a turbine which is typically connected to the spool via gearing. Compressed air is blown over the turbine of the air turbine starter, which causes the spool to rotate and start the gas turbine engine. After starting the gas turbine engine, the air turbine starter typically provides no useful function until the gas turbine engine needs to be started again. In the meantime, the air turbine starter just adds undesirable weight to a gas turbine engine, which is especially undesirable on an aircraft.
Gas turbine engines also typically have various components, such as gears and bearings, which benefit from lubrication and cooling. An oil supply system supplies oil, or another lubricating liquid, to and from the components to lubricate and cool the components. This oil is typically cooled by a heat exchanger positioned in a gas flow path. If the gas flow path has a relatively slow air flow, the heat exchanger typically needs to be relatively large and bulky to achieve the desired amount of cooling. A relatively large heat exchanger undesirably increases the weight of the aircraft. In gas turbine engines where the heat exchanger is positioned in a bypass flow stream of the engine's propulsion fan, the heat exchanger can also reduce overall thrust output.